Resin plug for wellbore abandonment

ABSTRACT

A resin plug for wellbore abandonment includes: an amount of a heavier resin and an amount of a light weight resin, the heavier resin configured to have a faster setting rate than the light weight resin. The resin plug creates a seal for wellbore abandonment by the heavier resin setting first followed by setting of the light weight resin thereafter. Any void formed during setting of the heavier resin is filled by the light weight resin before the light weight resin sets

FIELD

The present invention relates to a resin plug for wellbore abandonmentand method for placement.

BACKGROUND

Resin plugs are employed to seal off an abandoned well. The plug isintroduced as a liquid resin and is held in place in the well. The plugcreates a seal after the resin sets. Historically as a resin plughardens, minor shrinkage of the plug may occur. As a resin plug shrinks,it may pull away from the wellbore wall and creates a small gap betweenthe wellbore wall and the set resin. This shrinkage, and in particularthe resulting gap, effectively minimizes the resin plug's usefulness asa permanent barrier within a wellbore.

SUMMARY

In accordance with a broad aspect of the present invention, there isprovided a resin plug for wellbore abandonment comprising: an amount ofa heavier resin and an amount of a light weight resin, the heavier resinconfigured to have a faster setting rate than the light weight resin.

In accordance with another broad aspect of the present invention, thereis provided a method for placing a seal in a wellbore, the methodcomprising: placing a liquid resin in the wellbore, the liquid resinincluding an amount of a heavier resin and an amount of a light weightresin, the heavier resin configured to have a faster setting rate thanthe light weight resin, the heavier resin residing in the wellbore belowthe light weight resin; and the seal being formed by the heavier resinsetting first followed by setting of the light weight resin thereafter,wherein a void formed during setting of the heavier resin is filled bythe light weight resin before the light weight resin sets.

It is to be understood that other aspects of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein various embodiments of the invention areshown and described by way of illustration. As will be realized, theinvention is capable of other and different embodiments and its severaldetails are capable of modification in various other respects, allwithin the present invention. Accordingly the drawings and detaileddescription are to be regarded as illustrative in nature and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings, several aspects of the present invention areillustrated by way of example, and not by way of limitation, in detailin the figures, wherein:

FIGS. 1 and 2 are schematic views through a wellbore, according to oneaspect of the present invention, showing the plug at various stages,where FIG. 2 is later in time than FIG. 1.

FIG. 3 is an enlarged view of the final set plug of FIG. 2.

DESCRIPTION OF VARIOUS EMBODIMENTS

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentscontemplated by the inventor. The detailed description includes specificdetails for the purpose of providing a comprehensive understanding ofthe present invention. However, it will be apparent to those skilled inthe art that the present invention may be practiced without thesespecific details.

A resin plug for wellbore abandonment and a method of placement havebeen invented.

A resin plug can be placed and allowed to set in a wellbore. Whenintroduced to the well, a resin plug includes resin in a liquid state.After placement in the well, the liquid resin sets up, which is theresin's hardening phase, to a solid resin, such that the final resinplug is a solid in the well. With reference to the Figures, a resin plug10 according to one aspect of the present invention is shown in place ina well 12. FIG. 1 shows resin plug 10 at a time when the resin plug hasrecently been placed in a well 12 and the resin is still in the liquidstate, prior to setting up. FIGS. 2 and 3 show the resin plug 10 of FIG.1 after it has set up to a solid.

The present resin plug 10 includes two resins 10 a, 10 b, including: (i)a first amount of resin, called herein a light weight resin 10 a and asecond amount of resin, called herein a heavier resin 10 b, has (i) aweight greater and (ii) a setting rate faster than the light weightresin. The resin amounts are configured for placement in the wellbore ina liquid state and for set up in the well. The resin amounts areconfigured such that, when in a liquid state and placed in the wellbore,the heavier resin 10 b resides below (according to gravity) the lighterresin 10 a. Also, the heavier resin sets up more quickly than the lightweight resin such that while heavier resin 10 b sets up and becomes asolid, lighter resin 10 b above the heavier resin remains in a liquidstate for an amount of time after the heavier resin has set up. Thelight weight resin 10 a also eventually sets up to a solid state to formthe final resin plug. The present resin plug has therefore been termedherein as a 2-stage, weighted resin plug. The term 2-stage is usedherein to mean that the plug includes the two amounts of resin: theheavier resin and the lighter resin.

The resin plug is useful in various kinds of wells but it may beparticularly useful in a cased wellbore where well is lined with a liner14 such as casing.

The plug is held in place in the well until at least the heavier resinsets. As such, the plug may be placed on a platform such as a bridgeplug 16, packer, cement plug, or other structure within the well. Theplatform need not have significant pressure holding capabilities, butinstead simply is configured to hold the resin in place until it sets.

As noted above, prior resin plugs suffer from issues relating to resinshrinkage. The general function and purpose of a 2-stage weighted resinplug addresses the issue of resin shrinkage during its setup. Inparticular, since the heavier resin sets first, any gap G that developsdue to resin shrinkage can be filled by light weight resin 10 a flowinginto and substantially filling the gap before it also sets. The void,gap G, created by shrinkage of the heavier resin is generally betweenthe outer side surfaces of the hardened heavier resin plug and theconstraining walls of the wellbore, which in a cased well is the innerfacing wall of liner 14. The light weight resin, then, flows into thissemi- or fully annular space and thereafter hardens as a thin, semi- orfully annular filler, surrounding the hardened heavier resin plug.

The light weight resin 10 a and the heavier resin 10 b are any of themany resins suitable for wellbore sealing. Both resins, have a specificgravity that prevents them from floating and are durable in wellboreconditions. Both resins may have a viscosity that allows them to flowwhen in the liquid state, such as a viscosity similar to that of water.

A liquid resin can be configured for use as the heavier amount or thelight weight amount, respectively, by selection or modification of eachresin amount to create a weight and set-up rate differential between thetwo amounts. This may include selection of two different base resins ormodification of a single resin composition with respect to weightingagents and hardening chemicals to achieve the differential weight andsetup rate between light weight resin 10 a and heavier resin 10 b. Thetwo resins 10 a, 10 b may also have different viscosities or other phasedifferentiators.

In embodiments, the light weight resin may have a density of about 900to 1300 kg/m³ or 1050 to 1300 kg/m³ (specific gravity greater than waterand up to about 1.5) and the heavier resin has a density greater thanthat. Alternately or in addition, the light weight resin may have asetting time 10-20 times longer than the heavier resin. In oneembodiment for example, the heavier resin 10 b has a setting time of2-10, such as 4-8 hours, and the lighter resin has much longer timerequired for setting such as more than 40 hours or possibly even 60hours or more. The difference in setting time may be achieved in variousways, as will be appreciated. For example, in one embodiment, theheavier resin is configured to set faster than the light weight one byminor adjustments to the heavier resin recipe relative to the lighterresin recipe. For example, by adding a hardening agent to the heavierresin that is not present, or present in lower concentration, in thelighter resin.

In one embodiment, the two resins 10 a, 10 b are based on the sameresin: a vinyl ester resin, which include esters derived from vinylalcohol for example vinyl acetate, vinyl propionate and vinyl laureate.The heavier resin and the lighter resin are obtained by (i) adjustingtheir relative specific gravity by adding concentrations of a weightingagent such as barite and (ii) adjusting their relative hardening ratesby addition of a hardening agent (also sometimes called an initiator oran activator) such as, for example, one or more of aN-dimethyl-p-toluide or a dibenzoyl peroxide. In one embodiment, theheavier resin contains higher concentrations of both the weighting agentand the hardening agent than the lighter resin. The concentrationsprovide the heavier vinyl ester resin with a specific gravity of1.3-1.9, or possibly 1.5-1.7 specific gravity, and a hardening time of4-8 hours.

A method is based on delivering the 2-stage liquid resin to a pointwithin the wellbore to be abandoned and allowing the resin to setup toform the final plug and, thereby, to create a seal in the wellbore toprevent fluid communication from an accessed formation to surface.

The method includes: placing a liquid resin in the wellbore, the liquidresin including an amount of a heavier resin and an amount of a lightweight resin, the heavier resin configured to have a faster setting ratethan the light weight resin, the heavier resin residing in the wellborebelow the light weight resin. The seal is formed by setting of theheavier resin first followed thereafter by setting of the light weightresin. In the method, any external void, such as a semi- or fullyannular gap G between the heavier resin and the well's restraining wallsuch as liner 14, formed during setting of the heavier resin issubstantially filled by the light weight resin before setting thereof.The lighter resin substantially fills the gap and may also have at leasta portion thereof spanning the well inner diameter above the heavierresin.

In one embodiment of a method, the resins for a 2-stage resin plug areplaced in the well by employing a payload container. Both resins can beplaced in the well at the same time in one trip, if desired. Forexample, the two amounts of resin (the heavier resin and the lighterresin) are introduced to the payload container. The two resins are addedto the payload container with the heavier weighted resin placed withinthe payload container and the second light weight resin on top of theheavier resin. The heavier resin can be added to the container firstfollowed by the second, lighter one. The payload container is configuredfor running into the well to be abandoned.

The payload container is run in to a predefined depth within a wellbore,such as a steel cased 14 wellbore, and the 2 stage liquid resin isplaced into the wellbore. The resins flow out of the payload containerand fill a section of the well above a platform 16 on which they areplaced. The difference in weight between the two resins causes them tobecome positioned in two layers in the well with the lighter resinresiding on top of the heavier resin (FIG. 1). The resin amounts areconfigured for placement in the wellbore in a liquid state and will setup in the well. The resin amounts are configured such that, when placedin the wellbore, the heavier resin remains below the lighter resin.

The empty payload container is then recovered to surface. The payloadcontainer in one embodiment returns to surface by buoyancy through awater column in the well.

The lower stage heavy weighted resin 10 b has a quicker setup time thanthe upper stage lightweight resin 10 a. When the heavier weighted resinhardens, it has a slight shrinkage factor and thus a void, gap G, willbe created between the casing and the resulting hardened resin plug ofthe heavier resin.

The lighter resin, which is on top of the heavier resin, has a muchslower setup time and remains liquid after the heavier resin hashardened. Thus, once the bottom stage resin plug is set/hardens, thevoid is filled by a downward flow of upper stage, light weight resinliquid (FIG. 2). In particular, the lighter resin which remains liquiduntil after the heavier resin has set, can flow down to fill any voidcreated by shrinkage of the heavier resin. As the light weight upperstage resin sets up it adheres to the steel casing because the thicknessof the light weight resin in the void is so small that the effect ofshrinkage is practically eliminated. Together, the 2-stage resin, whenboth amounts of resin set, creates an impermeable plug that canwithstand high hydrostatic pressures.

Tests have been conducted on vinyl ester-based plugs where barite andhardening agents were used to select the weight and hardening rate ofthe heavier amount over the lighter amount. Such plugs were successfullypressure tested to 21 MPa.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to those embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein, but is to beaccorded the full scope consistent with the claims, wherein reference toan element in the singular, such as by use of the article “a” or “an” isnot intended to mean “one and only one” unless specifically so stated,but rather “one or more”. All structural and functional equivalents tothe elements of the various embodiments described throughout thedisclosure that are known or later come to be known to those of ordinaryskill in the art are intended to be encompassed by the elements of theclaims. Moreover, nothing disclosed herein is intended to be dedicatedto the public regardless of whether such disclosure is explicitlyrecited in the claims. No claim element is to be construed under theprovisions of 35 USC 112, sixth paragraph, unless the element isexpressly recited using the phrase “means for” or “step for”.

We claim:
 1. A resin plug for wellbore abandonment comprising: an amount of a heavier resin and an amount of a light weight resin, the heavier resin configured to have a faster setting rate than the light weight resin.
 2. The resin plug of claim 1 wherein the heavier resin and the light weight resin both include the same base resin and the heavier resin includes a higher concentration of a weighting agent and a higher concentration of a hardening agent than the light weight resin.
 3. The resin plug of claim 1 wherein the resin plug has a liquid state prior to setting into a hardened state and in the liquid state the amount of the heavier resin and the amount of the light weight resin are in separate layers with the amount of the heavier resin residing below the amount of the light weight resin.
 4. The resin plug of claim 3 wherein the resin plug in the hardened state has the amount of heavier resin hardened and the light weight resin substantially filling any external voids caused by shrinkage of the heavier resin.
 5. The resin plug of claim 4 wherein in the hardened state at least some external voids are between a wall of the wellbore and an outer side surface of the amount of heavier resin and a portion of the light weight resin is substantially filling the external voids.
 6. The resin plug of claim 1 wherein the light weight resin has a setting rate 10 to 20 times longer than the heavier resin.
 7. The resin plug of claim 1 wherein the heavier resin has a specific gravity of 1.3-1.9.
 8. A method for placing a seal in a wellbore, the method comprising: placing a liquid resin in the wellbore, the liquid resin including an amount of a heavier resin and an amount of a light weight resin, the heavier resin configured to have a faster setting rate than the light weight resin and after placing, the heavier resin residing in the wellbore below the light weight resin; and the seal being formed by the heavier resin setting first followed by setting of the light weight resin thereafter, wherein a void formed during setting of the heavier resin is filled by the light weight resin before the light weight resin sets.
 9. The method of claim 7 wherein the light weight resin has a setting rate 10 to 20 times longer than the heavier resin.
 10. The method of claim 8 wherein during placing the amount of the heavier resin and the amount of the light weight resin are placed in the well at the same time.
 11. The method of claim 8 wherein placing releases the liquid resin on a platform in the wellbore.
 12. The method of claim 8 wherein the void is between a wall of the wellbore and an outer side surface of the amount of heavier resin and a portion of the light weight resin flows to substantially fill the void.
 13. The method of claim 8 further comprising selecting the heavier resin to have a specific gravity of 1.3-1.9. 